1. Technical Field
The embodiment relates to an intake air temperature estimation system that is applied to a turbocharged engine including a compressor that compresses intake air and supplies the compressed intake air to a combustion chamber and that estimates the temperature of intake air after compression by the compressor.
2. Description of Related Art
Most of engines, such as vehicle-mounted engines, are provided with an air flow meter and an outside air temperature sensor. The air flow meter detects the volume flow rate of intake air in an intake passage. The outside air temperature sensor detects the temperature of outside air taken into the intake passage. The mass of intake air introduced into a combustion chamber, that is, the amount of air flowing into a cylinder, is obtained from detected results of the air flow meter and outside air temperature sensor.
On the other hand, in a turbocharged engine including a compressor that compresses intake air and supplies the compressed intake air to a combustion chamber, the temperature of intake air rises as the intake air is compressed by the compressor. As the temperature of intake air rises, the density of the intake air decreases. For this reason, in the turbocharged engine, in order to accurately estimate the amount of air flowing into a cylinder, it is required to acquire the temperature of intake air after compression by the compressor.
Conventionally, there is known a system described in Japanese Patent Application Publication No. 03-229952 (JP 03-229952 A) as an intake air temperature estimation system that estimates the temperature of intake air after compression by a compressor in a turbocharged engine. In the system described in JP 03-229952 A, an adiabatically compressed intake air temperature, which is a theoretical intake air temperature after compression by the compressor in an adiabatic state, is obtained from an intake air pressure and intake air temperature before compression by the compressor and an intake air pressure after compression by the compressor. The adiabatically compressed intake air temperature is corrected in response to a change in the intake air temperature due to the influence of engine load and engine rotation speed with the use of a correction coefficient set on the basis of the intake air pressure after compression and the engine rotation speed. Thus, an estimated value of the intake air temperature (estimated intake air temperature) after compression is obtained.